idnits 2.17.1 draft-ietf-pwe3-fat-pw-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** The document seems to lack a License Notice according IETF Trust Provisions of 28 Dec 2009, Section 6.b.i or Provisions of 12 Sep 2009 Section 6.b -- however, there's a paragraph with a matching beginning. Boilerplate error? (You're using the IETF Trust Provisions' Section 6.b License Notice from 12 Feb 2009 rather than one of the newer Notices. See https://trustee.ietf.org/license-info/.) Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 1, 2009) is 5406 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) ** Obsolete normative reference: RFC 4447 (Obsoleted by RFC 8077) == Outdated reference: A later version (-12) exists of draft-ietf-mpls-tp-framework-01 == Outdated reference: A later version (-10) exists of draft-ietf-mpls-tp-requirements-09 == Outdated reference: A later version (-02) exists of draft-kompella-mpls-entropy-label-00 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PWE3 S. Bryant, Ed. 3 Internet-Draft C. Filsfils 4 Intended status: Standards Track Cisco Systems 5 Expires: January 2, 2010 U. Drafz 6 Deutsche Telekom 7 V. Kompella 8 J. Regan 9 Alcatel-Lucent 10 S. Amante 11 Level 3 Communications 12 July 1, 2009 14 Flow Aware Transport of Pseudowires over an MPLS PSN 15 draft-ietf-pwe3-fat-pw-00 17 Status of this Memo 19 This Internet-Draft is submitted to IETF in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 This Internet-Draft will expire on January 2, 2010. 40 Copyright Notice 42 Copyright (c) 2009 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents in effect on the date of 47 publication of this document (http://trustee.ietf.org/license-info). 48 Please review these documents carefully, as they describe your rights 49 and restrictions with respect to this document. 51 Abstract 53 Where the payload carried over a pseudowire carries a number of 54 identifiable flows it can in some circumstances be desirable to carry 55 those flows over the equal cost multiple paths (ECMPs) that exist in 56 the packet switched network. Most forwarding engines are able to 57 hash based on label stacks and use this to balance flows over ECMPs. 58 This draft describes a method of identifying the flows, or flow 59 groups, to the label switched routers by including an additional 60 label in the label stack. 62 Requirements Language 64 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 65 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 66 document are to be interpreted as described in RFC2119 [RFC2119]. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 1.1. ECMP in Label Switched Routers . . . . . . . . . . . . . . 5 72 1.2. Flow Label . . . . . . . . . . . . . . . . . . . . . . . . 5 73 2. Native Service Processing Function . . . . . . . . . . . . . . 6 74 3. Pseudowire Forwarder . . . . . . . . . . . . . . . . . . . . . 6 75 3.1. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 7 76 4. Signaling the Presence of the Flow Label . . . . . . . . . . . 8 77 4.1. Structure of Flow Label TLV . . . . . . . . . . . . . . . 9 78 5. OAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 79 6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 10 80 6.1. ECMP . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 81 6.2. Link Aggregation Groups . . . . . . . . . . . . . . . . . 12 82 6.3. The Single Large Flow Case . . . . . . . . . . . . . . . . 12 83 6.4. MPLS-TP . . . . . . . . . . . . . . . . . . . . . . . . . 14 84 7. Applicability to MPLS . . . . . . . . . . . . . . . . . . . . 14 85 8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 86 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 87 10. Congestion Considerations . . . . . . . . . . . . . . . . . . 15 88 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 90 12.1. Normative References . . . . . . . . . . . . . . . . . . . 15 91 12.2. Informative References . . . . . . . . . . . . . . . . . . 16 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 94 1. Introduction 96 A pseudowire [RFC3985] is normally transported over one single 97 network path, even if multiple Equal Cost Multiple Paths (ECMP) exit 98 between the ingress and egress PEs[RFC4385] [RFC4928]. This is 99 required to preserve the characteristics of the emulated service 100 (e.g. to avoid misordering SAToP pseudowire packets [RFC4553] or 101 subjecting the packets to unusable inter-arrival times ). The use of 102 a single path to preserve order remains the default mode of operation 103 of a pseudowire (PW). The new capability proposed in this document 104 is an OPTIONAL mode which may be used when the use of ECMP paths for 105 is known to be beneficial (and not harmful) to the operation of the 106 PW. 108 Some pseudowires are used to transport large volumes of IP traffic 109 between routers at two locations. One example of this is the use of 110 an Ethernet pseudowire to create a virtual direct link between a pair 111 of routers. Such pseudowire's may carry from hundred's of Mbps to 112 Gbps of traffic. Such pseudowire's do not require strict ordering to 113 be preserved between packets of the pseudowire. They only require 114 ordering to be preserved within the context of each individual 115 transported IP flow. Some operators have requested the ability to 116 explicitly configure such a pseudowire to leverage the availability 117 of multiple ECMP paths. This allows for better capacity planning as 118 the statistical multiplexing of a larger number of smaller flows is 119 more efficient than with a smaller set of larger flows. Although 120 Ethernet is used as an example above, the mechanisms described in 121 this draft are general mechanisms that may be applied to any 122 pseudowire type in which there are identifiable flows, and in which 123 the there is no requirement to preserve the order between those 124 flows. 126 Typically, forwarding hardware can deduce that an IP payload is being 127 directly carried by an MPLS label stack, and is capable of looking at 128 some fields in packets to construct hash buckets for conversations or 129 flows. However, an intermediate node has no information on the type 130 pseudowire being carried in the packet. This limits the forwarder at 131 the intermediate node to only being able to make an ECMP choice based 132 on a hash of the label stack. In the case of a pseudowire emulating 133 a high bandwidth trunk, the granularity obtained by hashing the 134 default label stack is inadequate for satisfactory load-balancing. 135 The ingress node, however, is in the special position of being able 136 to look at the un-encapsulated packet and spread flows amongst an 137 available ECMP paths, or even Loop-Free Alternates I [RFC5286] . 138 This draft proposes a method to introduce granularity on the hashing 139 of traffic running over pseudowires by introducing an additional 140 label, chosen by the ingress node, and placed at the bottom of the 141 label stack. 143 In addition to providing an indication of the flow structure for use 144 in ECMP forwarding decisions, the mechanism described in the document 145 may also be used to select flows for distribution over an 802.1ad 146 link aggregation group that has been used in an MPLS network. 148 1.1. ECMP in Label Switched Routers 150 Label switched routers commonly hash the label stack or some elements 151 of the label stack as a method of discriminating between flows, in 152 order to distribute those flows over the available equal cost 153 multiple paths that exist in the network. Since the label at the 154 bottom of stack is usually the label most closely associated with the 155 flow, this normally provides the greatest entropy, and hence is 156 usually included in the hash. This draft describes a method of 157 adding an additional label at the bottom of stack in order to 158 facilitate the load balancing of the flows within a pseudowire over 159 the available ECMPs. A similar design for general MPLS use has also 160 been proposed [I-D.kompella-mpls-entropy-label], however that is 161 outside the scope of this draft. 163 An alternative method of load balancing by creating a number of 164 pseudowires and distributing the flows amongst them was considered, 165 but was rejected because: 167 o It did not introduce as much entropy as the load balance label 168 method. 170 o It required additional pseudowires to be set up and maintained. 172 1.2. Flow Label 174 An additional label is interposed between the pseudowire label and 175 the control word, or if the control word is not present, between the 176 pseudowire label and the pseudowire payload. This additional label 177 is called the Flow label. Indivisible flows within the pseudowire 178 MUST be mapped to the same Flow label by the ingress PE. The flow 179 label stimulates the correct ECMP load balancing behaviour in the 180 PSN. On receipt of the pseudowire packet at the egress PE (which 181 knows this additional label is present) the flow label is discarded 182 without processing. 184 Note that the flow label MUST NOT be an MPLS reserved label (values 185 in the range 0..15) [RFC3032], but is otherwise unconstrained by the 186 protocol. 188 Considerations of the TTL value are described in the Security section 189 of this document. The flow label can never become the top label in 190 normal operation, and hence the TTL in the flow label is never used 191 to determine whether the packet should be discarded due to TTL 192 expiry. Therefore there are no lower restrictions on the TTL value. 194 2. Native Service Processing Function 196 The Native Service Processing (NSP) function [RFC3985] is a component 197 of a PE that has knowledge of the structure of the emulated service 198 and is able to take action on the service outside the scope of the 199 pseudowire. In this case it is required that the NSP in the ingress 200 PE identify flows, or groups of flows within the service, and 201 indicate the flow (group) identity of each packet as it is passed to 202 the pseudowire forwarder. As an example, where the PW type is an 203 Ethernet, the NSP might parse the ingress Ethernet traffic and 204 consider all of the IP traffic. This traffic could then be 205 categorized into flows by considering all traffic with the same 206 source and destination address pair to be a single indivisible flow. 207 Since this is an NSP function, by definition, the method used to 208 identify a flow is outside the scope of the pseudowire design. 209 Similarly, since the NSP is internal to the PE, the method of flow 210 indication to the pseudowire forwarder is outside the scope of this 211 document. 213 3. Pseudowire Forwarder 215 The pseudowire forwarder must be provided with a method of mapping 216 flows to load balanced paths. 218 The forwarder must generate a label for the flow or group of flows. 219 How the load balance label values are determined is outside the scope 220 of this document, however the load balance label allocated to a flow 221 MUST NOT be an MPLS reserved label and SHOULD remain constant for the 222 life of the flow. It is recommended that the method chosen to 223 generate the load balancing labels introduces a high degree of 224 entropy in their values, to maximise the entropy presented to the 225 ECMP path selection mechanism in the LSRs in the PSN, and hence 226 distribute the flows as evenly as possible over the available PSN 227 ECMP paths. The forwarder at the ingress PE prepends the pseudowire 228 control word (if applicable), and then pushes the flow label, 229 followed by the pseudowire label. 231 The forwarder at the egress PE uses the pseudowire label to identify 232 the pseudowire. From the context associated with the pseudowire 233 label, the egress PE can determine whether a flow label is present. 234 If a flow label is present, the label is discarded. 236 All other pseudowire forwarding operations are unmodified by the 237 inclusion of the flow label. 239 3.1. Encapsulation 241 The PWE3 Protocol Stack Reference Model modified to include flow 242 label is shown in Figure 1 below 244 +-------------+ +-------------+ 245 | Emulated | | Emulated | 246 | Ethernet | | Ethernet | 247 | (including | Emulated Service | (including | 248 | VLAN) |<==============================>| VLAN) | 249 | Services | | Services | 250 +-------------+ +-------------+ 251 | Flow | | Flow | 252 +-------------+ Pseudowire +-------------+ 253 |Demultiplexer|<==============================>|Demultiplexer| 254 +-------------+ +-------------+ 255 | PSN | PSN Tunnel | PSN | 256 | MPLS |<==============================>| MPLS | 257 +-------------+ +-------------+ 258 | Physical | | Physical | 259 +-----+-------+ +-----+-------+ 261 Figure 1: PWE3 Protocol Stack Reference Model 263 The encapsulation of a pseudowire with a flow label is shown in 264 Figure 2 below 265 +-------------------------------+ 266 | MPLS Tunnel label(s) | n*4 octets (four octets per label) 267 +-------------------------------+ 268 | PW label | 4 octets 269 +-------------------------------+ 270 | Flow label | 4 octets 271 +-------------------------------+ 272 | Optional Control Word | 4 octets 273 +-------------------------------+ 274 | Payload | 275 | | 276 | | n octets 277 | | 278 +-------------------------------+ 280 Figure 2: Encapsulation of a pseudowire with a pseudowire load 281 balancing label 283 4. Signaling the Presence of the Flow Label 285 When using the signalling procedures in [RFC4447], there is a 286 Pseudowire Interface Parameter Sub-TLV type used to synchronize the 287 flow label states between the ingress and egress PEs. 289 The absence of a flow label (FL) TLV by either party indicates that 290 the PE concerned is unable to recognize this TLV and the sender of 291 the FL TLV MUST send a new label mapping without the FL TLV. This 292 preserves backwards compatibility with existing PEs that do not 293 understand the FL TLV or that cannot, do not wish to, process the 294 flow label. 296 A PE that wishes to use a flow label sends an FL TLV with the F bit 297 set. A PE that can correctly process a flow label and is willing to 298 receive on, but does not wish to send a flow label sends an FL TLV 299 with the F bit clear. A PE that sends an FL TLV with the F bit set 300 and receives an FL TLV with or without the F bit set MUST include the 301 flow label between the pseudowire label and the control word (or is 302 the control word is not present between the pseudowire label and the 303 pseudowire payload). 305 If PWE3 signalling [RFC4447] is not in use for a pseudowire, then 306 whether the flow label is used MUST be identically provisioned in 307 both PEs at the pseudowire endpoints. If there is no provisioning 308 support for this option, the default behaviour is not to include the 309 flow label. 311 Note that what is signalled is the desire to include the flow label 312 in the label stack. The value of the label is a local matter for the 313 ingress PE, and the label value itself is not signalled. 315 4.1. Structure of Flow Label TLV 317 The structure of the flow label TLV is shown in Figure 3. 319 0 1 2 3 320 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 | FL | Length |F| must be zero | 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 Figure 3: Multiple VC TLV 327 Where: 329 o FL is the flow label TLV identifier assigned by IANA. 331 o Length is the length of the TLV in octets and is 4. 333 o When F=1 a flow label will be pushed. When F=0 a flow label will 334 not be pushed. 336 5. OAM 338 The following OAM considerations apply to this method of load 339 balancing. 341 Where the OAM is only to be used to perform a basic test that the 342 pseudowires have been configured at the PEs, VCCV [RFC5085] messages 343 may be sent using any load balance pseudowire path, i.e. using any 344 value for the flow label. 346 Where it is required to verify that a pseudowire is fully functional 347 for all flows, VCCV [RFC5085] connection verification message MUST be 348 sent over each ECMP path to the pseudowire egress PE. This problem 349 is difficult to solve and scales poorly. We believe that this 350 problem is addressed by the following two methods: 352 1. If a failure occurs within the PSN, this failure will normally be 353 detected by the PSN's Interior Gateway protocol (IGP) (link/node 354 failure, link or BFD or IGP hello detection), and the IGP 355 convergence will naturally modify the ECMP set of network paths 356 between the Ingress and Egress PE's. Hence the PW is only 357 impacted during the normal IGP convergence time. 359 2. If the failure is related to the individual corruption of an 360 Label Forwarding Information dataBase (LFIB) entry in a router, 361 then only the network path using that specific entry is impacted. 362 If the PW is load balanced over multiple network paths, then this 363 failure can only be detected if, by chance, the transported OAM 364 flow is mapped onto the impacted network path, or all paths are 365 tested. This type of error may be better solved be solved by 366 other means such as LSP self test [I-D.ietf-mpls-lsr-self-test]. 368 To troubleshoot the MPLS PSN, including multiple paths, the 369 techniques described in [RFC4378] and [RFC4379] can be used. 371 Where the pseudowire OAM is carried out of band (VCCV Type 2) it is 372 necessary to insert an "MPLS Router Alert Label" in the label stack. 373 The resultant label stack is a follows: 375 +-------------------------------+ 376 | MPLS Tunnel label(s) | n*4 octets (four octets per label) 377 +-------------------------------+ 378 | Router Alert label | 4 octets 379 +-------------------------------+ 380 | PW label | 4 octets 381 +-------------------------------+ 382 | Flow label | 4 octets 383 +-------------------------------+ 384 | Optional Control Word | 4 octets 385 +-------------------------------+ 386 | Payload | 387 | | 388 | | n octets 389 | | 390 +-------------------------------+ 392 Figure 4: Use of Router Alert LAbel 394 6. Applicability 396 A node within the PSN is not able to perform deep-packet-inspection 397 (DPI) of the PW as the PW technology is not self-describing: the 398 structure of the PW payload is only known to the ingress and egress 399 PE devices. The method proposed in this document provides a 400 statistical mitigation of the problem of load balance in those cased 401 where a PE is able to discern flows embedded in the traffic received 402 on the attachment circuit. 404 The methods describe in this document are transparent to the PSN and 405 as such do not require any new capability from the PSN. 407 The requirement to load-balance over multiple PSN paths occurs when 408 the ratio between the PW access speed and the PSN's core link 409 bandwidth is large (e.g. >= 10%). ATM and FR are unlikely to meet 410 this property. Ethernet does and this is the reason why this 411 document focuses on Ethernet. Applications for other high-access- 412 bandwidth PW's (fiber-channel) may be defined in the future. 414 This design applies to MPLS pseudowires where it is meaningful to 415 deconstruct the packets presented to the ingress PE into flows. The 416 mechanism described in this document promotes the distribution of 417 flows within the pseudowire over different network paths. This in 418 turn means that whilst packets within a flow are delivered in order 419 (subject to normal IP delivery perturbations due to topology 420 variation), order is not maintained amongst packets of different 421 flows. It is not proposed to associate a different sequence number 422 with each flow. If sequence number support is required this 423 mechanism is not applicable. 425 Where it is known that the traffic carried by the Ethernet pseudowire 426 is IP the method of identifying the flows are well known and can be 427 applied. Such methods typically include hashing on the source and 428 destination addresses, the protocol ID and higher-layer flow- 429 dependent fields such as TCP/UDP ports, L2TPv3 Session ID's etc. 431 Where it is known that the traffic carried by the Ethernet pseudowire 432 is non-IP, techniques used for link bundling between Ethernet 433 switches may be reused. In this case however the latency 434 distribution would be larger than is found in the link bundle case. 435 The acceptability of the increased latency is for further study. Of 436 particular importance the Ethernet control frames SHOULD always be 437 mapped to the same PSN path to ensure in-order delivery. 439 6.1. ECMP 441 ECMP in packet switched networks is statistical in nature. The 442 mapping of flows to a particular path does not take into account the 443 bandwidth of the flow being mapped or the current bandwidth usage of 444 the members of the ECMP set. This simplification works well when the 445 distribution of flows is evenly spread over the ECMP set and there 446 are a large number of flows that have low bandwidth relative to the 447 paths. A random allocation of a flow to a path provides a good 448 approximation to an even spread provided polarization effects are 449 avoided. The method proposed in this document has the same 450 statistical properties as an IP PSN. 452 ECMP is a load-sharing mechanism that is based on sharing the load 453 over a number of layer 3 paths through the PSN. Often however 454 multiple links exist between a pair of LSRs that are considered by 455 the IGP to be a single link. These are known as link bundles. The 456 mechanism described in this document can also be used to distribute 457 the flows within a pseudowire over the members of the link bundle by 458 using the flow label value to identify candidate flows. How that 459 mapping takes place is outside the scope of this specification. 460 Similar considerations apply to link aggregation groups. 462 In the ECMP case and the link bundling case the NSP may attempt to 463 take bandwidth into consideration when allocating groups of flows to 464 a common path. That is permitted, but it must be borne in mind that 465 the semantics of a label stack entry (LSE) as defined by [RFC3032] 466 cannot be modified, the value of the flow label cannot be modified at 467 any point on the LSP, and the interpretation of bit patterns in or 468 values of the flow label by an LSR are undefined. 470 A different type of load balancing is the desire to carry a 471 pseudowire over a set of PSN links in which the bandwidth of members 472 of the link set is less than the bandwidth of the pseudowire. This 473 problem is addressed in [I-D.stein-pwe3-pwbonding]. Such a mechanism 474 can be considered complementary to this mechanism. 476 6.2. Link Aggregation Groups 478 A Link Aggregation Group (LAG) is used to bond together several 479 physical circuits between two adjacent nodes so they appear to 480 higher-layer protocols as a single, higher bandwidth "virtual" pipe. 481 These may co-exist in various parts of a given network. An advantage 482 of LAGs is that they reduce the number of routing and signaling 483 protocol adjacencies between devices, reducing control plane 484 processing overhead. As with ECMP key problem related to LAG is, due 485 to inefficiencies in LAG load-distribution algorithms, a particular 486 component- link may experience congestion, and the mechanism proposed 487 here may be able to assist in producing a more uniform flow 488 distribution. 490 The same considerations requiring a flow to go over a single member 491 of an ECMP path set apply to a member of a LAG. 493 6.3. The Single Large Flow Case 495 Clearly the operator should make sure that the service offered using 496 PW technology and the method described in this document does not 497 exceed the maximum planned link capacity unless it can be guaranteed 498 that it conforms to the Internet traffic profile of a very large 499 number of small flows. 501 If the payload on a PW is made of a single inner flow (i.e. an 502 encrypted connection between two routers), or the flow identifiers 503 are too deeply buried in the packet then the functionality described 504 in this document does not give any benefits, though neither does it 505 cause harm relative to the existing situation. The most common case 506 where a single flow dominated the traffic on a PW is when it is used 507 to transport enterprise traffic. Enterprise traffic may well consist 508 of a large single TCP flows , or encrypted flows that cannot be 509 handled by the methods described in this document. 511 An operator has six options under these circumstances: 513 1. The operator can do nothing and the system will work as it does 514 without the flow label. 516 2. The operator can make the customer aware that the service 517 offering has a restriction on flow bandwidth and police flows to 518 that restriction. This would allow customers offering multiple 519 flows to use a larger fraction their access bandwidth, whilst 520 preventing an single flow from consuming a fraction of internal 521 link bandwidth that the operator considered excessive. 523 3. The operator could configure the ingress PE to assign a constant 524 flow label to all high bandwidth flows so that only one path was 525 affected by these flows, 527 4. The operator could configure the ingress PE to assign a random 528 flow label to all high bandwidth flows so as to minimise the 529 disruption to the network as a cost of out of order traffic to 530 the user. 532 5. The operator could configure the ingress to assign a label of 533 special significance to all high bandwidth flows so that some 534 other action (not specified in this document) could be taken on 535 the flow. 537 The issues described above are mitigated by the following two 538 factors: 540 o Firstly, the customer of a high-bandwidth PW service has an 541 incentive to get the best transport service because an inefficient 542 use of the PSN leads to jitter and eventually to loss to the PW's 543 payload. 545 o Secondly, the customer is usually able to tailor their 546 applications to generate many flows in the PSN. A well-known 547 example is massive data transport between servers which use many 548 parallel TCP sessions. This same technique can be used by any 549 transport protocol: multiple UDP ports, multiple L2TPv3 Session 550 ID's, multiple GRE keys may be used to decompose a large flow into 551 smaller components. This approach may be applied to IPsec where 552 multiple SPI's may be allocated to the same security association. 554 6.4. MPLS-TP 556 The MPLS Transport Profile (MPLS-TP) [I-D.ietf-mpls-tp-requirements], 557 [I-D.ietf-mpls-tp-framework] requirement 44 states that "MPLS-TP MUST 558 support mechanisms which ensure the integrity of the transported 559 customer's service traffic as required by its associated SLA. Loss 560 of integrity may be defined as packet corruption, re-ordering or loss 561 during normal network conditions". The flow aware transport of a PW 562 reorders packets (albeit in an application friendly way) and 563 therefore SHOULD NOT be deployed in a network conforming to the 564 MPLS-TP. 566 7. Applicability to MPLS 568 A further application of this technique would be to create a basis 569 for hash diversity without having to peek below the label stack for 570 IP traffic carried over LDP LSPs. Work on the generalization of this 571 to MPLS has been described in [I-D.kompella-mpls-entropy-label]. 572 This is can be regarded as a complementary but distinct approach 573 since although similar consideration may apply to the identification 574 of flows and the allocation of flow label values, the flow labels are 575 imposed by different network components and the associated signalling 576 mechanisms are different. 578 8. Security Considerations 580 The pseudowire generic security considerations described in [RFC3985] 581 and the security considerations applicable to a specific pseudowire 582 type (for example, in the case of an Ethernet pseudowire [RFC4448] 583 apply. 585 The ingress PE SHOULD take steps to ensure that the load-balance 586 label is not used as a covert channel. 588 It is useful to give consideration to the choice of TTL value in the 589 flow label LSE. Since the flow label is the bottom of stack and even 590 when PHP is employed will on arrival at the egress PE be prepended by 591 the PW label, the flow label TTL MAY be set to a value of 1. This 592 will prevent the packet being inadvertently forwarded based on the 593 value of the flow label. Note that this may be a departure from 594 considerations that apply to the general MPLS case. 596 9. IANA Considerations 598 IANA is requested to allocate the next available values from the IETF 599 Consensus range in the Pseudowire Interface Parameters Sub-TLV type 600 Registry as a Flow Label indicator. 602 Parameter Length Description 604 TBD 4 Load Balancing Label 606 10. Congestion Considerations 608 The congestion considerations applicable to pseudowires as described 609 in [RFC3985] and any additional congestion considerations developed 610 at the time of publication apply to this design. 612 The ability to explicitly configure a PW to leverage the availability 613 of multiple ECMP paths is beneficial to capacity planning as, all 614 other parameters being constant, the statistical multiplexing of a 615 larger number of smaller flows is more efficient than with a smaller 616 number of larger flows. 618 Note that if the classification into flows is only performed on IP 619 packets the behaviour of those flows in the face of congestion will 620 be as already defined by the IETF for packets of that type and no 621 additional congestion processing is required. 623 Where flows that are not IP are classified pseudowire congestion 624 avoidance must be applied to each non-IP load balance group. 626 11. Acknowledgements 628 The authors wish to thank Eric Grey, Kireeti Kompella, Joerg 629 Kuechemann, Wilfried Maas, Luca Martini, Mark Townsley, and Lucy Yong 630 for valuable comments on this document. 632 12. References 634 12.1. Normative References 636 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 637 Requirement Levels", BCP 14, RFC 2119, March 1997. 639 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 640 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 641 Encoding", RFC 3032, January 2001. 643 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 644 Label Switched (MPLS) Data Plane Failures", RFC 4379, 645 February 2006. 647 [RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, 648 "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for 649 Use over an MPLS PSN", RFC 4385, February 2006. 651 [RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. 652 Heron, "Pseudowire Setup and Maintenance Using the Label 653 Distribution Protocol (LDP)", RFC 4447, April 2006. 655 [RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron, 656 "Encapsulation Methods for Transport of Ethernet over MPLS 657 Networks", RFC 4448, April 2006. 659 [RFC4553] Vainshtein, A. and YJ. Stein, "Structure-Agnostic Time 660 Division Multiplexing (TDM) over Packet (SAToP)", 661 RFC 4553, June 2006. 663 [RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal 664 Cost Multipath Treatment in MPLS Networks", BCP 128, 665 RFC 4928, June 2007. 667 [RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit 668 Connectivity Verification (VCCV): A Control Channel for 669 Pseudowires", RFC 5085, December 2007. 671 12.2. Informative References 673 [I-D.ietf-mpls-lsr-self-test] 674 Swallow, G., "Label Switching Router Self-Test", 675 draft-ietf-mpls-lsr-self-test-07 (work in progress), 676 May 2007. 678 [I-D.ietf-mpls-tp-framework] 679 Bocci, M., Bryant, S., and L. Levrau, "A Framework for 680 MPLS in Transport Networks", 681 draft-ietf-mpls-tp-framework-01 (work in progress), 682 June 2009. 684 [I-D.ietf-mpls-tp-requirements] 685 Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., 686 and S. Ueno, "MPLS-TP Requirements", 687 draft-ietf-mpls-tp-requirements-09 (work in progress), 688 June 2009. 690 [I-D.kompella-mpls-entropy-label] 691 Kompella, K. and S. Amante, "The Use of Entropy Labels in 692 MPLS Forwarding", draft-kompella-mpls-entropy-label-00 693 (work in progress), July 2008. 695 [I-D.stein-pwe3-pwbonding] 696 Stein, Y., Mendelsohn, I., and R. Insler, "PW Bonding", 697 draft-stein-pwe3-pwbonding-01 (work in progress), 698 November 2008. 700 [RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to- 701 Edge (PWE3) Architecture", RFC 3985, March 2005. 703 [RFC4378] Allan, D. and T. Nadeau, "A Framework for Multi-Protocol 704 Label Switching (MPLS) Operations and Management (OAM)", 705 RFC 4378, February 2006. 707 [RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast 708 Reroute: Loop-Free Alternates", RFC 5286, September 2008. 710 Authors' Addresses 712 Stewart Bryant (editor) 713 Cisco Systems 714 250 Longwater Ave 715 Reading RG2 6GB 716 United Kingdom 718 Phone: +44-208-824-8828 719 Email: stbryant@cisco.com 721 Clarence Filsfils 722 Cisco Systems 723 Brussels 724 Belgium 726 Email: cfilsfil@cisco.com 727 Ulrich Drafz 728 Deutsche Telekom 729 Muenster, 730 Germany 732 Phone: 733 Fax: 734 Email: Ulrich.Drafz@t-com.net 735 URI: 737 Vach Kompella 738 Alcatel-Lucent 740 Phone: 741 Fax: 742 Email: Alcatel-Lucent vach.kompella@alcatel-lucent.com 743 URI: 745 Joe Regan 746 Alcatel-Lucent 748 Phone: 749 Fax: 750 Email: joe.regan@alcatel-lucent.comRegan 751 URI: 753 Shane Amante 754 Level 3 Communications 756 Phone: 757 Fax: 758 Email: shane@castlepoint.net 759 URI: